<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <!-- 加个defer属性 -->
    <script defer src="./index.js"></script>
    <style>
        /* 小球的基本样式 */
        .ball{
            background-color: aqua;
            border-radius: 50%;
            width: 20px;
            height: 20px;
            position: absolute;
            left: 0px;
            top: 0px;
        }

        /* 容器元素：作为小球移动的范围 */
        #t1{
            width: 500px;
            height: 400px;
            border: 1px solid black;
            position: relative;
        }
    </style>
</head>
<body>
    <div id="t1">
        <div id="ball" class="ball"></div>   
        <!-- <script src="./index.js"></script> -->
    </div>

    <button id="btnStart">Start</button>
    <button id="btnStop">Stop</button>
    

</body>
</html>
